Battery charging circuits have long been designed for reacharging lead-acid and other types of rechargable cells employing a number of particular well known types of control circuitry. Typically, such chargers require a rectifier, such as a bridge rectifier, to obtain a direct current or interrupted direct current from an alternating source such as line voltage. The rectifier output is coupled to some type of regulation circuit in the form of either a constant voltage regulator or a constant circuit regulator ahead of the cell to be charged. Constant voltage regulators often use a Zener diode as the reference voltage source and may employ a current limiter to limit the charging current to the battery at the near constant voltage. Simple shunt diode circuits having a predetermined forward voltage drop may be used as the simplest form of constant voltage regulator in a charging circuit. It is also been known to employ an operational amplifier in connection with a Zener diode regulated charger.
Another general charger is the constant current charger employing a diode or rectifier and a current limiting resistor. This type of simple constant current charger has one major disadvantage, and that is excessive power loss and heat generated in the current limiting resistor and, in fact, it does not limit current to a constant value.
It has long been recognized that it is desirable for a charger to operate not only to recharge a cell at the most rapid safe rate, but also to maintain a float or trickle charge on the battery at all times. In certain types of cells, such as the lead-gel or lead-dioxide cell, the maintainance of a float potential across the battery terminal produces much longer life and assured full charge whenever required.
Despite this well developed state of the art, I have found that existing charger circuits fail to truly regulate the charging current within allowable limits, both in the charge and float or trickle charge condition, resulting in either the danger of overcharge and gassing or damage to the cell or loss than optimum charging. I have discovered that this occurs because none of the constant voltage chargers which I have been able to analyze actually maintain a constant voltage across the battery terminals or either charge or flow, and even more seriously, do not accurately limit the charging current. Additionally, constant current type chargers, from my examination, do not actually maintain a constant current and further fail to respond to a full charge condition to convert or switch from the full charge to a float condition.
For certain types of cells which have open cells and are charged in a relatively cool location, the deficiencies in charging systems have relatively little noticable effect. When, however, precise batteries such as the lead-gel or lead-lead dioxide cell and other cells which are sealed are improperly charged, irreparable damage to the cell can occur. Faced with these limitations on the prior art, I have invented an improved charging system for batteries.